Controller for RF power generator with reduced cable length sensitivity

Abstract

A radio frequency (RF) power generator system includes a power generator that generates a RF power signal that is output to a load. The RF generator generates a forward power feedback signal and a reverse power feedback signal. A controller receives the forward power feedback signal and the reverse power feedback signal. The controller generates a setpoint signal that is output to the power generator. A setpoint modifier receives the forward feedback signal, the reverse feedback signal and an external setpoint signal. The setpoint modifier calculates a forward power limit based on the forward and reverse power feedback signals. The setpoint modifier and outputs a modified setpoint signal to the controller based on one of the forward power limit and the external setpoint signal. The setpoint modifier and the controller can be integrated.

What is claimed is:  
     
       1. A radio frequency (RF) power generator system, comprising: 
       a power generator that generates a RF power signal that is output to a load, a forward power feedback signal and a reverse power feedback signal;  
       a controller that receives said forward power feedback signal and said reverse power feedback signal and that generates a setpoint signal that is output to said power generator; and  
       a setpoint modifier that receives said forward feedback signal, said reverse feedback signal and an external setpoint signal, wherein said setpoint modifier calculates a forward power limit based on said forward and reverse feedback signals and outputs a modified setpoint signal to said controller based on one of said forward power limit and said external setpoint signal.  
     
     
       2. The RF power generator system of  claim 1  wherein said controller selects a lesser value of said forward power limit and said external setpoint signal as said modified setpoint signal. 
     
     
       3. The RF power generator system of  claim 2  wherein said power generator includes a RF sensor that generates said forward power feedback signal and said reverse power feedback signal. 
     
     
       4. The RF power generator system of  claim 3  wherein power generator includes power module that generates a supply current feedback signal and a temperature feedback signal that are output to said controller. 
     
     
       5. The RF power generator system of  claim 3  wherein said setpoint modifier and said controller are integrated. 
     
     
       6. The RF power generator system of  claim 5  wherein said setpoint modifier includes one of a lookup table and a formula for calculating said forward power limit from said forward and reverse feedback signals. 
     
     
       7. The RF power generator system of  claim 6  wherein said power generator includes a power amplifier and wherein said formula determines said forward power limit based on gamma and at least one of maximum power dissipation supply current, supply voltage and output voltage of said power amplifier. 
     
     
       8. A method of controlling a radio frequency (RF) power generator that generates a RF power signal for a load, comprising the steps of: 
       sensing a forward power feedback signal;  
       sensing a reverse power feedback signal;  
       receiving an external setpoint signal;  
       calculating a forward power limit based on said forward and reverse power feedback signals; and  
       controlling said RF power generator based on one of said forward power limit and said external setpoint signal.  
     
     
       9. The method of  claim 8  further comprising the step of: 
       selecting a lesser value of said forward power limit and said external setpoint signal; and  
       transmitting said lesser value to a power module.  
     
     
       10. The method of  claim 9  further comprising the step of: 
       generating said forward power feedback signal and said reverse power feedback signal using an RF sensor in said RF power generator.  
     
     
       11. The method of  claim 10  further comprising the step of: 
       generating a supply current feedback signal and a temperature feedback signal using said power module of said RF power generator.  
     
     
       12. The method of  claim 8  wherein said forward power limit is calculated using one of a lookup table and a formula. 
     
     
       13. The method of  claim 12  wherein said power generator includes a power amplifier and wherein said formula defines a relationship between gamma, said forward power limit, and at least one of power dissipation, supply current, supply voltage and output voltage of said power amplifier. 
     
     
       14. The method of  claim 13  wherein said formula is calculated by: 
       a) identifying a cable length between 0 and one-half wavelength with a highest power dissipation at a first VSWR;  
       b) repeating step (a) for a plurality of VSWRs;  
       c) for each of said VSWRs, determining a mathematical approximation of power dissipation as a function of forward power for said cable length having said highest power dissipation; and  
       d) parameterizing said mathematical approximation as a function of one of VSWR and gamma.  
     
     
       15. The method of  claim 14  wherein said mathematical approximation is a linear approximation. 
     
     
       16. A method of controlling a radio frequency (RF) power generator that generates a RF power signal for a load to reduce sensitivity to variations in a cable length between said RF power generator and said load, comprising the steps of: 
       a) identifying a cable length between 0 and one-half wavelength with a highest power dissipation at a first VSWR;  
       b) repeating step (a) for a plurality of VSWRs;  
       c) for each of said VSWRs, determining a mathematical approximation of power dissipation as a function of forward power for said cable length having said highest power dissipation;  
       d) parameterizing said mathematical approximations as a function of gamma;  
       e) defining a forward power limit formula based on said parameterization; and  
       f) programming a controller with said forward power limit formula.  
     
     
       17. The method of  claim 16  further comprising the steps of: 
       sensing a forward power feedback signal; and  
       sensing a reverse power feedback signal.  
     
     
       18. The method of  claim 17  further comprising the steps of: 
       receiving an external setpoint signal; and  
       calculating a forward power limit based on said forward power limit formula.  
     
     
       19. The method of  claim 18  further comprising the steps of: 
       controlling said RF power generator based on said forward power limit and said external setpoint signal.  
     
     
       20. The method of  claim 19  further comprising the step of: 
       generating a modified setpoint signal equal to a lesser value of said forward power limit and said external setpoint signal.